1. Field of Invention
The field of the currently claimed embodiments of this invention relates to active optical beam shaping systems and methods, and more particularly to active optical beam shaping systems and methods using sequential deformable mirrors.
2. Discussion of Related Art
Exo-planetary systems that are directly imaged using existing facilities (Marois et al. 2008; Kalas et al. 2008; Lagrange et al. 2010) give a unique laboratory to constrain planetary formation at wide separations (Rafikov 2005; Dodson-Robinson et al. 2009; Kratter et al. 2010; Johnson et al. 2010), to study the planetary luminosity distribution at critical young ages (Spiegel & Burrows 2012; Fortney et al. 2008) and the atmospheric properties of low surface gravity objects (Barman et al. 2011b,a; Marley et al. 2010; Madhusudhan et al. 2011). Upcoming surveys, conducted with instruments specifically designed for high-contrast (Dohlen et al. 2006; Graham et al. 2007; Hinkley et al. 2011), will unravel the bulk of this population of self-luminous Jovian planets and provide an unprecedented understanding of their formation history. Such instruments will reach the contrast required to achieve their scientific goals by combining Extreme Adaptive Optics systems (Ex-AO, Poyneer & V'eran (2005)), optimized coronagraphs (Soummer et al. 2011; Guyon 2003; Rouan et al. 2000) and nanometer class wavefront calibration (Sauvage et al. 2007; Wallace et al. 2009; Pueyo et al. 2010). In the future, high-contrast instruments on Extremely Large Telescopes will focus on probing planetary formation in distant star forming regions (Macintosh et al. 2006), characterizing both the spectra of cooler gas giants (V'erinaud et al. 2010) and the reflected light of planets in the habitable zone of low mass stars. The formidable contrast necessary to investigate the presence of biomarkers at the surface of earth analogs (>1010) cannot be achieved from the ground beneath atmospheric turbulence and will require dedicated space-based instruments (Guyon 2005).
The coronagraphs that will equip upcoming Ex-AO instruments on 8 meter class telescopes have been designed for contrasts of at most ˜10−7. Secondary support structure (or spiders: 4 struts each 1 cm wide, ˜0.3% of the total pupil diameter in the case of Gemini South) have a small impact on starlight extinction at such levels of contrasts. In this case, coronagraphs have thus been optimized on circularly symmetric apertures, which only take into account the central obscuration (Soummer et al. 2011). However, high-contrast instrumentation on future observatories will not benefit from such gentle circumstances. ELTs will have to support a substantially heavier secondary than 8 meter class observatories do, and over larger lengths: as a consequence, the relative area covered by the secondary support will increase by a factor of 10 (30 cm wide spiders, occupying ˜3% of the pupil diameter in the case of TMT). This will degrade the contrast of coronagraphs only designed for circularly obscured geometries by a factor ˜100, when the actual envisioned contrast for an ELT exo-planet imager can be as low as ˜10−8 (Macintosh et al. 2006). While the trade-offs associated with minimization of spider width in the space-based case have yet to be explored, secondary support structures will certainly hamper the contrast depth of coronagraphic instruments of such observatories at levels that are well above the 1010 contrast requirement. As a consequence, telescope architectures currently envisioned for direct characterization of exo-earths consist of monolithic, off-axis, and thus un-obscured, telescopes (Guyon et al. 2008; Trauger et al. 2010). Coronagraphs for such architectures take advantage of the pupil symmetry to reach a theoretical contrast of ten orders of magnitude (Guyon et al. 2005; Vanderbei et al. 2003a,b; Kasdin et al. 2005; Mawet et al, 2010; Kuchner & Traub 2002; Soummer et al. 2003). However, using obscured on-axis and/or segmented apertures take full advantage of the limited real estate associated with a given launch vehicle and can allow larger apertures that increase the scientific return of space-based direct imaging survey. Recent solutions can mitigate the presence of secondary support structures in on-axis apertures. However these concepts present practical limitations: APLCs on arbitrary apertures (Soummer et al. 2009) and Shaped Pupils (Carlotti et al. 2011) suffer from throughput loss for very high contrast designs, and PIAAMCM (Guyon et al. 2010a) rely on a phase mask technology whose chromatic properties have not yet been fully characterized. Moreover, segmentation will further complicate the structure of the telescope's pupil: both the amplitude discontinuities created by the segments gaps and the phase discontinuities resulting from imperfect phasing will thus further degrade coronagraphic contrast. Devising a practical solution for broadband coronagraphy on asymmetric, unfriendly apertures is an outstanding problem in high contrast instrumentation. Therefore, there remains a need for improved beam shaping systems and methods.